The basic concept of a compressor using pairs of involute spiral scrolls is a venerable one at this point. As shown in FIGS. 17 through 19, which are taken from a 1905 U.S. Pat. No. 801,182 to Creux, an involute scroll, indicated generally at 10, is generated by a non stretchable line 12 being unwrapped from around the circumference of a so called generating circle 14 of radius Rg. The string, being held at one fixed point, constitutes a so called swing radius, and traces out the spiral involute or curve shown. If stopped at any point, the line formed by the string, (several such equally spaced lines are shown in FIG. 17) called a swing radius line, is not the same length as it would be stopped at any other point, because it is being unwound. FIG. 17 shows a single line to represent the spiral, which, obviously, does not represent well an object that could exist in reality. However, as shown in FIG. 18 simply regenerating the same spiral with a slightly shorter string, shorter by an amount "t", generates a second, congruent spiral curve line, giving an inner surface and an outer surface, termed inner and outer wraps 16 and 18. The wraps 16 and 18 run from an inner edge 20 to an outer edge 22. Scroll 10 covers only one complete turn, or 360 degrees, from edge 20 to edge 22, although it could, if desired, cover more. In practice, scrolls generally will cover more than one turn, at least one and a half turns, for practical reasons. As shown in FIG. 19, if these wraps 16 and 18 are in turn bounded by parallel, axially spaced planes represented by a disk shaped end plate 24 and an axial end edge 26, a complete scroll 10 results.
In FIG. 20 two scrolls of the general type described above, but covering one and a half turns each, are indicated generally at 28 and 30. These, if interfitted by reversing one and axially pushing them one within the other, followed by angularly offsetting them by 180 degrees and radially offsetting them by a distance Ro (defined below) will create at least two (here, four) lines of contact between the juxtaposed inner and outer wraps. These lines of contact, in turn, define two pockets, indicated by shading. The distance Ro is defined as (P/2)-t, where P is the so called pitch of the scroll, which, in turn, is equal to the circumference of the generating circle described above. If one scroll is fixed while the other is orbited about the axis of the fixed scroll with the orbit radius Ro maintained, as indicated in FIG. 20, then all parts of the orbiting scroll, such as the point near the outer edge illustrated, rotate in a circle of radius Ro. If, during orbiting, some mechanism also prevents the scrolls from relatively rotating, then the lines of contact will shift along the wrap surfaces continually inwardly, shrinking the pockets continually inwardly and then reforming them at the rim of the outer rim of the scrolls. This creates a theoretically simple compressor, with low pressure gas introduced to the pockets at the rim and squeezed continually down toward the center.
While the above description sets out the general theory of the scroll compressor, its practical application has involved decades of learning how to actually machine the scroll and of developing workable, cost effective mechanisms to orbit the scroll at the orbit radius, to prevent the orbiting scroll from rotating relative to the fixed scroll as it orbits, and to assemble all of the components of the various mechanisms into proper alignment. The drive mechanism, almost universally, is an eccentric crank which drives the orbital scroll about the fixed scroll with the appropriate orbit radius. An example of this general drive mechanism can be see in essentially any scroll compressor patent, in one form or another. Design work has focused on new ways to manufacture and counterbalance the eccentric crank, as well as to provide a measure of radial yield to accommodate scroll wear or contaminant particles between the contacting scroll wraps. An example may be seen in co assigned U.S. Pat. No. 5,366,360 to Bookbinder et al. But the basic operation of the eccentric crank is little changed. The anti rotation mechanism (the means that maintains the proper angular offset between the scrolls in operation) is more diverse, but is most often either an Oldham ring, an example of which is disclosed in U.S. Pat. No. 4,484,869 or a ball coupling mechanism, an example of which is also disclosed in the co assigned '360 patent. Other anti rotation mechanisms have been proposed, but all have the same basic function of allowing the orbiting scroll to orbit with the proper radius, while preventing it from rotating as it does so. The primary drawback of all anti-rotation mechanism is the large number of components that comprise, which are costly and occupy space within the compressor, as well as the great difficulty during assembly in getting all the components properly relatively aligned. This is especially true of the standard ball coupling mechanisms, which requires numerous pins and slots to properly align the ball races.